High pressure pump

Abstract

A gas chamber is placed adjacent to a variable volume chamber of a high pressure pump. The gas chamber includes an inner blocking wall, which borders on the variable volume chamber and contacts fuel in the variable volume chamber, an outer blocking wall, which is opposed to the inner blocking wall, and gas, which fills a space that is defined between the inner blocking wall and the outer blocking wall.

1 . A high pressure pump comprising:
 a plunger;   a pump body that includes:
 a cylinder hole, in which the plunger is adapted to reciprocate in an axial direction thereof; 
 a pressurizing chamber, which is communicated with the cylinder hole and in which fuel is pressurized by reciprocating movement of the plunger; 
 a low pressure fuel passage, which communicates between the pressurizing chamber and a fuel inlet; and 
 a discharge passage, which communicates between the pressurizing chamber and a fuel outlet; 
   variable volume chamber forming means for forming a variable volume chamber, a volume of which changes by the reciprocating movement of the plunger, wherein the variable volume chamber is placed adjacent to a step surface of the plunger, and the step surface of the plunger is located between a large diameter portion of the plunger, which has an end portion exposed to the pressurizing chamber and is slidable along an inner peripheral wall surface of the cylinder hole, and a small diameter portion of the plunger, which extend from the large diameter portion in the axial direction on a side opposite from the pressurizing chamber; and   a gas chamber that is placed adjacent to the variable volume chamber on a side of the variable volume chamber, which is opposite from the cylinder hole.   
     
     
         2 . The high pressure pump according to  claim 1 , wherein the gas chamber includes:
 an inner blocking wall, which borders on the variable volume chamber and contacts fuel in the variable volume chamber;   an outer blocking wall, which is opposed to the inner blocking wall; and   gas, which fills a space that is defined between the inner blocking wall and the outer blocking wall.   
     
     
         3 . The high pressure pump according to  claim 2 , wherein the inner blocking wall is made of a resiliently deformable member. 
     
     
         4 . The high pressure pump according to  claim 2 , wherein:
 one end portion of the inner blocking wall extends in a direction generally perpendicular to a central axis of the cylinder hole;   a wall surface of the one end portion of the inner blocking wall, which is located on a side where the pressurizing chamber is located, is opposed to the step surface of the plunger;   a seal member is installed to surround the small diameter portion of the plunger in a circumferential direction; and   an opposite wall surface of the one end portion of the inner blocking wall, which is located on an opposite side that is opposite from the pressurizing chamber, contacts an end portion of the seal member, which is located on a side where the pressurizing chamber is located.   
     
     
         5 . The high pressure pump according to  claim 2 , wherein the outer blocking wall is a seal element, which is fixed to the pump body. 
     
     
         6 . The high pressure pump according to  claim 2 , wherein the outer blocking wall is made of a heat insulation member. 
     
     
         7 . The high pressure pump according to  claim 2 , wherein the inner blocking wall is a seal element, which is fixed to the pump body. 
     
     
         8 . The high pressure pump according to  claim 2 , wherein:
 the inner blocking wall is welded to the outer blocking wall; and   the gas is sealed in the space, which is a closed space and is defined between the inner blocking wall and the outer blocking wall.   
     
     
         9 . The high pressure pump according to  claim 2 , wherein the gas is one of nitrogen gas, helium gas, argon gas and air. 
     
     
         10 . The high pressure pump according to  claim 2 , wherein:
 the low pressure fuel passage includes a damper chamber, which is formed in the pump body and receives a pulsation damper that is adapted to damp pressure pulsation of fuel in the damper chamber; and   the variable volume chamber is in fluid communication with the damper chamber through a return passage formed in the pump body.   
     
     
         11 . The high pressure pump according to  claim 2 , wherein:
 a plunger stopper is joined to the pump body on an axial side of the plunger stopper where the pressurizing chamber is located;   the plunger stopper is adapted to abut against the step surface of the plunger when the plunger is moved in a direction away from a top dead center of the plunger;   a seal member is installed to surround the small diameter portion of the plunger in a circumferential direction on an axial side of the plunger stopper, which is opposite from the pressurizing chamber in the axial direction;   the seal member is axially clamped between the plunger stopper and one of the inner blocking wall and the outer blocking wall; and   the plunger stopper includes at least one radial passage, through which a radially inner portion of the variable volume chamber located on a radially inner side of the plunger stopper is in fluid communication with a radially outer portion of the variable volume chamber located on a radially outer side of the plunger stopper.